Aquarium filter



FIG. 1 is a top perspective view of an aquarium filter according to the present invention;

FIG. 2 is a rear view thereof thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is a bottom view thereof.

Elements depicted with broken lines do not constitute portions of the claimed design. 

The ornamental design for an aquarium filter, as shown and described. 